Recent mobile phones are often equipped with two antennas, a main antenna and a sub-antenna, to ensure their telephone conversation quality. An advantage of being equipped with two antennas is to prevent degradation of telephone conversation quality using the other antenna even if the user touches one antenna, which would otherwise result in the degradation of the telephone conversation quality.
An example of the folding mobile phone equipped with such two antennas is illustrated in FIG. 1.
The conventional folding mobile phone illustrated in FIG. 1 comprises an upper housing 1, a lower housing 2, a hinge unit 3, a main antenna 4 located in the vicinity of the hinge unit 3 of the lower housing 2, and a sub-antenna 5 located at the lower end of the lower housing 2. In addition, the upper housing 1 contains an upper circuit board 6, a display 11, etc., while the lower housing 2 contains a main antenna 4, a sub-antenna 5, a lower circuit board 7, a battery 12, etc.
For example, for such configured folding mobile phone, Patent Document 1 discloses a method for ensuring characteristics of the main antenna 4 located at the hinge unit 3. In this document, the case material of both of the upper housing 1 and the lower housing 2 is composed of an insulation material such as mold. In addition, an upper-and-lower-circuits connecting unit 8, which connects the upper circuit board 6 with the lower circuit board 7, is located at and wound once around the hinge unit 3, so that it has an inductance and reduces the amount of high-frequency current that flows between the upper circuit board 6 and the lower circuit board 7, thereby electrically separating the upper circuit board 6 from the lower circuit board 7.
[Patent Document 1]: Japanese Patent Laid-Open No. 2002-27066 (pages 8-13 and FIG. 1)
While it is possible to ensure the antenna characteristics in the above method in case of the antennas that are mounted in the vicinity of the hinge unit, the characteristics of the sub-antenna that is located at the end opposite to the hinge unit would not necessarily be optimized in the condition where the upper circuit board and the lower circuit board are electrically separated from each other.
FIG. 2 illustrates the antenna characteristics (radiation characteristics) of each of the main antenna that is located in the vicinity of the hinge unit of the lower housing and the sub-antenna that is located at the end opposite to the hinge unit of the lower housing in the following cases: when an electrical connection state between the upper circuit board and the lower circuit board is OPEN (unconnected); and when it is SHORT (connected). As illustrated, it can be seen that the main antenna that is located in the vicinity of the hinge unit will yield better characteristics in OPEN, while the sub-antenna that is located at the end opposite to the hinge unit will yield better characteristics in SHORT.
In the conventional folding mobile phones, however, the electrical connection state between the upper circuit board and the lower circuit board is often maintained in OPEN due to the design in favor of the characteristics of the main antenna located in the vicinity of the hinge unit. In such a connection state, the sub-antenna characteristics could no longer be improved and problems could arise that cause the degradation of telephone conversation quality when the sub-antenna is used.
The present invention is provided in view of the above problems, and a main object thereof is to provide a folding mobile phone that may improve the antenna characteristics of both of a main antenna and a sub-antenna.